Solar thermal conversion gels for atmospheric water harvesting: fundamental principles and applications

To address freshwater scarcity, solar-driven adsorption-based atmospheric water harvesting (AWH) has emerged as a promising technological route because of its low energy demand, broad climatic adaptability, and potential for decentralized operation. Among the candidate materials, solar thermal conversion gels integrate three key functions within a single platform, namely hygroscopic water capture, water storage and transport, and solar-thermal-driven desorption, and are therefore regarded as one of the most promising high-performance material systems for AWH. This review systematically summarizes recent progress in salt-based solar thermal conversion gels for AWH, including their design principles and compositions (hygroscopic components, gel networks, and solar thermal components), and discusses in depth the physicochemical mechanisms governing adsorption and desorption. It further summarizes key performance indicators (such as adsorption/desorption kinetics, daily water production, and cycling stability) together with corresponding optimization strategies (such as structural engineering, component regulation, and system/energy management). In addition, the review highlights diverse application scenarios, including portable water collectors, large-scale water harvesting farms, smart response systems, and synergistic integration with other emerging technologies (such as radiative cooling). Finally, this review analyzes the current challenges facing AWH and provides an outlook on future research directions in this field, including smart gel materials, biomimetic design, and multi-energy coupling.